The Japanese Utility Model Application Laid-Open Publication No. 57-129110 discloses a burr-removing tool for inserting a tool into a hole of a work, removing foreign material from within the hole, and confirming a depth of the hole. The burr-removing tool will be described based on FIGS. 7 and 8 hereof.
A burr-removing tool 100 shown in FIG. 7 comprises a base 101; a hydraulic cylinder 102 that is attached to the base 101; an air case 104 retractably provided by the hydraulic cylinder 102 and a slidable supporting member 103, 103; and a plurality of tools 105 retractably attached to the air case 104. The air case 104 comprises a partitioned chamber A, chamber D, and chamber P. Compressed air is supplied to the chamber A and chamber P. A pressure switch 106 is provided in the chamber D.
FIG. 8(a) to (c) show the air case 104 and the tool 105 being advanced by the hydraulic cylinder 102, the tool 105 being inserted into a hole 108 of the work W, the compressed air of the chamber A being discharged from a leading end 105a through a hole 105h of the tool 105, the foreign material within the hole 108 being removed, and the depth of the hole being detected.
As shown in FIG. 8(a), the tool 105 is urged in an advancing direction by the compressed air of the chamber P when the depth Ds of the hole 108 is normal; therefore, the tool 105 is not displaced with respect to the air case 104. Accordingly, the pressure of chamber D does not change and the pressure switch 106 is not activated; therefore, the depth of the hole 108 is judged to be normal.
As shown in FIG. 8(b), the leading end 105a of the tool 105 hits the bottom of the hole 108 when the depth Da of the hole 108 is less as the reference. Furthermore, when the air case 104 is advanced by the hydraulic cylinder 102, only the air case 104 advances while the tool 105 remains stopped. Therefore, the tool 105 reaches a state of being retracted by displacement h. The compressed air in chamber P flows into chamber D via holes 111, 112, and 113 in the stated order. The air pressure is detected by the pressure switch provided to the chamber D, whereby the depth of the hole is judged to be abnormal.
The tool 105 is in the shape of a syringe needle, and is made of a relatively thin, hollow material; therefore, the leading end may break. The ability for the burr-removing tool 100 to detect such a fault is investigated below.
As shown in FIG. 8(c), a tool 105 having a broken leading end 105a is inserted into the hole 108, whose depth Da is less than the standard depth. The leading end 105a of the tool 105 does not make contact with the bottom of the hole 108. The pressure of the chamber D does not change at this time because the tool 105 does not retract. The pressure switch 106 is accordingly not activated; therefore, the depth of the hole is judged to be normal. A major problem is thus presented in that the depth of the hole is judged to be normal even when it is actually abnormal, and erroneous judgments of this kind need to be eliminated.